1. Field of the Invention
The present invention relates to electronic devices, and more specifically to devices for switching radio frequency signals.
2. Description of Related Art
Devices for switching radio frequency signals are very important components in radio frequency systems that have multiple operating modes. Exemplary systems include reception and transmission systems, such as GSM telephones and radio frequency head remote controls. Such switching devices can be used to specify which path a radio frequency signal should follow according to the selected mode of operation. They can also be used to connect or disconnect system components to and from one another (e.g., switching an antenna between the receiver and the transmitter of a radio frequency device). They can also be used to enable or disable certain components as a function of the selected mode (e.g., an attenuator or an amplifier).
Conventional mechanical switching devices have satisfactory isolation performance but suffer from extremely slow switching speeds and very high costs. Conventional switching devices using gallium arsenide components perform satisfactorily but also suffer from very high costs. On the other hand, conventional switching devices based on MOS transistors integrated on an electronic chip occupy a considerable amount of space on the chip and also suffer from high costs while providing relatively poor performance.
A MOS transistor acting as a switch is normally connected so as to transmit signals between its drain and source, while being controlled by a voltage applied to its gate. If the voltage Vgs between the gate and the source is below a threshold voltage Vt, the transistor is referred to as xe2x80x9coffxe2x80x9d and there is no conduction between the drain and source. If the voltage Vgs is above the threshold voltage Vt, a conducting channel forms between the drain and the source to allow a signal to pass. However, the resistance between the drain and source of such a MOS transistor is proportional to the distance between the drain and source, and inversely proportional to the product of the width times the thickness between the drain and source. In order to obtain a drain-source resistance of low value, in particular the reference value of 50 ohms that constitutes the typical input resistance of the downstream circuits, it is necessary to provide a very wide channel zone.
In view of these drawbacks, it is an object of the present invention to overcome the above-mentioned drawbacks and to provide a switching device that has a more efficient and improved performance.
It is another object of the present invention to provide a switching device that is inexpensive.
Still another object of the present invention is to provide a switching device that takes up little space on an electronic chip.
One embodiment of the present invention provides a device for switching radio frequency signals. The device includes at least a first MOS transistor for selectively interrupting or transmitting the signals between at least first and second terminals as a function of a control signal. The gate of the first MOS transistor is connected to the first terminal, and both the drain and source of the first MOS transistor are connected to the second terminal. In a preferred embodiment, the first MOS transistor selectively interrupts or transmits the signals between the first terminal and the second terminal, and the device also includes a second MOS transistor for selectively interrupting or transmitting the signals between the first terminal and a third terminal.
Another embodiment of the present invention provides a system for processing radio frequency signals. The system includes at least one device for switching radio frequency signals, and the device includes at least a first MOS transistor for selectively interrupting or transmitting the signals between at least first and second terminals of the system as a function of a control signal. The gate of the first MOS transistor is connected to the first terminal, and both the drain and source of the first MOS transistor are connected to the second terminal.